[perf] Fast path for coercions

[compiler-errors]

Check if the goal holds before trying to walk through the goal. If it certainly holds (or certainly does not), then don't select anything.

[compiler-errors]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 41aaf68 with merge 840dfe0…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 840dfe0 (840dfe0e6a8015d92e12916e9eaa11641c1909cf, parent: d1d8e386c5e84c4ba857f56c3291f73c27e2d62a)

[rust-timer]

Finished benchmarking commit (840dfe0): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.2%, 0.7%]	17
Regressions ❌ (secondary)	1.5%	[0.2%, 6.3%]	46
Improvements ✅ (primary)	-0.8%	[-2.7%, -0.2%]	32
Improvements ✅ (secondary)	-1.4%	[-4.0%, -0.2%]	41
All ❌✅ (primary)	-0.4%	[-2.7%, 0.7%]	49

Max RSS (memory usage)

Results (primary 0.7%, secondary -1.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.2%	[1.2%, 3.6%]	7
Regressions ❌ (secondary)	3.1%	[1.0%, 6.0%]	6
Improvements ✅ (primary)	-1.3%	[-1.9%, -0.7%]	5
Improvements ✅ (secondary)	-3.5%	[-6.8%, -1.1%]	11
All ❌✅ (primary)	0.7%	[-1.9%, 3.6%]	12

Cycles

Results (primary -3.0%, secondary -1.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.5%	[1.2%, 5.1%]	10
Improvements ✅ (primary)	-3.0%	[-3.9%, -1.2%]	7
Improvements ✅ (secondary)	-3.3%	[-5.1%, -1.2%]	29
All ❌✅ (primary)	-3.0%	[-3.9%, -1.2%]	7

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 692.944s -> 692.949s (0.00%)
Artifact size: 372.01 MiB -> 372.04 MiB (0.01%)

[compiler-errors]

Ok so this is an improvement at least in the new trait solver, but only ~3%. I'll probably table this for now, because it also requires us to dramatically overhaul how we do diagnostics.

[compiler-errors]

Actually, what if we only check if the goal holds certainly... 🤔

[compiler-errors]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 92b2f28 with merge f8500ef…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: f8500ef (f8500efe4e5b6b71fbc809554e79843db41613cc, parent: 8de4c7234dd9b97c9d76b58671343fdbbc9a433e)

[rust-timer]

Finished benchmarking commit (f8500ef): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.2%, 1.9%]	106
Regressions ❌ (secondary)	2.2%	[0.1%, 9.0%]	112
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	2
Improvements ✅ (secondary)	-0.9%	[-1.1%, -0.8%]	3
All ❌✅ (primary)	0.6%	[-0.2%, 1.9%]	108

Max RSS (memory usage)

Results (primary 1.6%, secondary -1.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.9%	[0.6%, 3.1%]	11
Regressions ❌ (secondary)	2.4%	[1.3%, 3.5%]	5
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	1
Improvements ✅ (secondary)	-4.4%	[-8.4%, -1.1%]	8
All ❌✅ (primary)	1.6%	[-1.5%, 3.1%]	12

Cycles

Results (primary 1.5%, secondary 4.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.0%, 2.6%]	24
Regressions ❌ (secondary)	4.6%	[1.8%, 7.4%]	28
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.5%	[1.0%, 2.6%]	24

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 691.904s -> 694.234s (0.34%)
Artifact size: 372.02 MiB -> 371.52 MiB (-0.14%)